Bacterial communities colonize epithelial surfaces of most animals. Several factors, including the innate immune system, mucus composition, and diet, have been identified as determinants of host-associated bacterial communities. Here we show that the early branching metazoan is able to modify bacterial quorum-sensing signals. We identified a eukaryotic mechanism that enables to specifically modify long-chain 3-oxo-homoserine lactones into their 3-hydroxy-HSL counterparts. Expression data revealed that 's main bacterial colonizer, sp., responds differentially to -(3-hydroxydodecanoyl)-l-homoserine lactone (3OHC12-HSL) and-(3-oxododecanoyl)-l-homoserine lactone (3OC12-HSL). Investigating the impacts of the different -acyl-HSLs on host colonization elucidated that 3OHC12-HSL allows and 3OC12-HSL represses host colonization of sp. These results show that an animal manipulates bacterial quorum-sensing signals and that this modification leads to a phenotypic switch in the bacterial colonizers. This mechanism may enable the host to manipulate the gene expression and thereby the behavior of its bacterial colonizers.

No abstract

Spatial clustering of enzymes has proven an elegant approach to optimize metabolite transfer between enzymes in synthetic metabolic pathways. Among the multiple methods used to promote colocalisation, enzyme fusion is probably the simplest. Inspired by natural systems, we have explored the metabolic consequences of spatial reorganizations of the catalytic domains of Xanthophyllomyces dendrorhous carotenoid enzymes produced in Saccharomyces cerevisiae. Synthetic genes encoding bidomain enzymes composed of CrtI and CrtB domains from the natural CrtYB fusion were connected in the two possible orientations, using natural and synthetic linkers. A tridomain enzyme (CrtB, CrtI, CrtY) harboring the full β-carotene producing pathway was also constructed. Our results demonstrate that domain order and linker properties considerably impact both the expression and/or stability of the constructed proteins and the functionality of the catalytic domains, all concurring to either diminish or boost specific enzymatic steps of the metabolic pathway. Remarkably, the yield of β-carotene production doubled with the tridomain fusion while precursor accumulation decreased, leading to an improvement of the pathway efficiency, when compared to the natural system. Our data strengthen the idea that fusion of enzymatic domains is an appropriate technique not only to achieve spatial confinement and enhance the metabolic flux but also to produce molecules not easily attainable with natural enzymatic configurations, even with membrane bound enzymes.

Inflammasomes are cytosolic protein complexes, which orchestrate the maturation of active IL‐1β by proteolytic cleavage via caspase‐1. Although many principles of inflammasome activation have been described, mechanisms that limit inflammasome‐dependent immune responses remain poorly defined. Here, we show that the thiol‐specific peroxidase peroxiredoxin‐4 (Prdx4) directly regulates IL‐1β generation by interfering with caspase‐1 activity. We demonstrate that caspase‐1 and Prdx4 form a redox‐sensitive regulatory complex via caspase‐1 cysteine 397 that leads to caspase‐1 sequestration and inactivation. Mice lacking Prdx4 show an increased susceptibility to LPS‐induced septic shock. This effect was phenocopied in mice carrying a conditional deletion of Prdx4 in the myeloid lineage (Prdx4‐ΔLysMCre). Strikingly, we demonstrate that Prdx4 co‐localizes with inflammasome components in extracellular vesicles (EVs) from inflammasome‐activated macrophages. Purified EVs are able to transmit a robust IL‐1β‐dependent inflammatory response in vitro and also in recipient mice in vivo. Loss of Prdx4 boosts the pro‐inflammatory potential of EVs. These findings identify Prdx4 as a critical regulator of inflammasome activity and provide new insights into remote cell‐to‐cell communication function of inflammasomes via macrophage‐derived EVs.

The nematode Caenorhabditis elegans interacts with a variety of bacteria as it feeds on microbes, and a number of these both associate and persist within the worm's intestine. Host-microbe interactions in C. elegans have been analyzed primarily at the transcriptome level with the host response often been monitored after challenge with pathogens. We assessed the proteome of C. elegans after growth on bacteria capable of colonizing its gut, via a comparative analysis of the nematode exposed to two naturally associated Ochrobactrum spp. (MYb71, MYb237) versus C. elegans grown on Escherichia coli OP50. A total of 4677 C. elegans proteins were identified, 3941 quantified. Significant alterations in protein abundances were observed for 122 proteins, 48 higher and 74 lower in abundance. We observed an increase in abundance of proteins potentially regulated via host signaling pathways, in addition to proteins involved in processing of foreign entities (e.g., lipase, proteases, glutathione metabolism). Decreased in abundance were proteins involved in both degradation and biosynthesis of amino acids, and enzymes associated with the degradation of peptidoglycan (lysozymes). The protein level differences between C. elegans grown on native microbiome members compared to the laboratory food bacterium may help to identify molecular processes involved in host-microbe interactions.